The present invention relates to systems for percutaneously delivering and deploying vascular stents and grafts, and more particularly to devices for positioning a stent or graft within a target vessel, then radially expanding the stent or graft into intimate contact with vessel tissue.
Stenosed vessels traditionally have been opened by angioplasty, with a balloon placed into the stenosed vessel and expanded radially to open the vessel. A frequently recurring problem with angioplasty is the eventual restenosis of the vessel. One approach to counteract restenosis involves positioning radially expandable stents within treated vessels. Typically, balloons are used to open the vessel wall and to expand the stent. However, size and burst pressure considerations limit the efficacy of balloons in expanding the stent. Multiple balloons typically are used to expand a single stent, due to the tendency of balloons to burst during stent expansion.
Another vessel condition requiring treatment, the aneurysm, results from weak blood vessel walls which can balloon due to the intrinsic pressure in the vessel. Aneurysms can apply pressure on adjacent anatomic structures, producing abnormal function. In addition, vessels have a potential to rupture, causing internal bleeding and potentially life threatening conditions. Grafts are used to isolate aneurysms or other blood vessel abnormalities from the blood pool, reducing pressure on the weakened vessel wall. Grafts reduce blood loss in the event of vessel rupture. Currently, grafts are expanded into place using balloon catheters. Some large diameter vessels, e.g. the aorta, require large diameter balloons to fully expand the graft into place. At the same time, the balloon must be collapsible into a low delivery profile during introduction and withdrawal, a factor that limits balloon diameters and wall thicknesses.
Frequently, calcified lesions result in weakened blood vessel wall sections, where a stent or graft must be radially expanded at a gradual rate to minimize the risk of further injury to the vessel. However, the paramount concern of maintaining blood flow through the vessel necessitates either providing a profusion lumen, or periodic evacuations of the balloon to allow blood flow, thus prolonging the radial expansion procedure.
Thus, a need exists for a mechanical delivery system which, in the non-linear environment found within blood vessels, is capable of expanding into an enlarged, predetermined configuration to cause an accompanying stent or graft to fully expand. The delivery system must facilitate introduction of a stent or graft into the target vessel, permit enlargement of the stent or graft within small vessels, and facilitate continuous profusion of blood around the expanding device during the procedure. The system also must be capable of exerting large radial forces to expand stents or grafts having excessive stiffness, or more generally to expand any grafts or stents within excessively stenosed vessels.
Particularly, there is a need for a delivery system which can expand stents or grafts without the need of an inflation medium. The delivery system must be capable of targeting large vessels such as the aorta, or small vessels such as the arteries or arterioles. Although the delivery system and particularly its stent or graft expansion region can be scaled to different sizes, preferably a single device or system is usable over a wide range of vessel and prosthesis sizes.